Measurement of torque and related parameters are extremely important capabilities in a number of transportation and industrial applications. Measuring the torque or strain on a mechanical element such as a drive shaft can be used in HUMS (Health and Usage Monitoring Systems) to determine the used and available lifetime of the component, and in real-time use may be used to warn the operator of the vehicle or equipment that they are approaching some limit of operation.
The basic methods available to measure or monitor torque typically center around use of a strain gage element(s) with a required power supply/signal connections and strategic gage placement opportunity on the target member or serially loaded component elements. All though useful in many instances, there are inherent limitations and applications challenges. Surface preparation and adherence methods for use of traditional strain gages sometimes alter or constrain the part or its assembled version. These sensors tend to be fragile devices that can be over stressed with a hysteresis affect causing a permanent shift to the strain gage characteristics affecting calibration values or can result in complete device failure. Such components must also be bound to the component to be monitored in a manner which effectively unites the gauge with the component as a single unit, so that the strain experienced by the component is directly and fully transferred to the gauge.
When the component to be monitored is a rotating device, other hurdles are added. Required performance often entails successful coupling of the power from the outside instrumentation amps to the target component and the retrieval of signal data generated on the part while not adversely altering its functional use. Slip rings were the early principal method of implementation in such cases. That method has susceptibilities to vibration, contact wear, contamination and heat generation from contact friction.
To address some of the slip ring vulnerability issues, a wireless variant of such devices, often utilizing transformer coupling of power and signal from the housing to the shaft, still share some of the burdens of its near cousin using slip rings: Physical limitation to tolerated movement of monitored element to the surrounding housing/coupling mechanics of the slip ring/sensor pickup assembly; and the use of bearings to support assemblies around the shaftlike element substituted for a length of the original part to be monitored. These devices have a large space allocation requirement and add to frictional losses along with rotational speed limit specifications that can constrain its application.
Optical type systems tend to be expensive and not tolerant to optical contamination from the many possible sources including normal environmental dust particles; dirt may obscure the markings, objects, or emitters used by the sensor, or it may cover/degrade the performance of the sensing elements themselves. These methods cannot be used where oils or others commonplace contaminants would obscure the optical performance.
Use of newer technologies, such as magnetic signature modeling and magnetic strain detection, require substitution of prime components with parts constructed of exotic materials and extensive instrumentation. The negative impact for the user can be dramatic: new processes, significant engineering time for design and calculations, potential certification issues and practical use limitations of material characteristics to perform the intended task are some of the most significant issues. These become even more significant when the component in question is part of an established system and manufacturing process; any change to, for example, the established design of components of a widely-used vehicle impacts the physical manufacturing and also the vehicle safety and certification areas of the industry.
Attempts have been made to mitigate the above issues by using rings or sensing components attached to the original component. This has the advantage of not requiring the entire manufacturing process to be changed, but still requires permanent physical modification of the component, as in order to register the changes in stress the rings or sensing components must be rigidly and effectively immovably bonded to the original component.
In addition, measurement of a magnetic field as a noncontact method tends to be limited by most methods to very small “lift-off” levels—small fractions of an inch. In many cases a shaft to be instrumented may require ¼″ or greater clearance around it due to movement in use, and this is much greater than the practical ranges for many such magnetic measurement-based devices.
The presented invention offers a new and innovative means of measuring torque with no physical connections to the measured component, no direct modification of the measured component, significant liftoff (greater than ¼″), and wireless, accurate acquisition of the data with no moving components in the system except for the shaft itself. The invention may also be applied to other stressed objects which move during the intervals in which stress or torque would be measured.